Conventionally, a mobile station computes a channel quality indicator (CQI) without considering the quality of service (QoS) present and/or available on a wireless channel over which the mobile station and a base station (BS) communicate. When asked to calculate a CQI, a conventional mobile station may calculate one modulation and coding scheme (MCS) based on fixed assumptions that may not reflect actual or desired operating conditions.
QoS describes desired characteristics for a channel to deliver a specific type of traffic. Different channels may have different QoS and one channel may even offer different QoS at different times. While CQI refers to a measurement of the quality of a channel, QoS refers to desired requirements for communication on a channel. QoS can be described using parameters including, but not limited to, a maximum acceptable packet delay, a maximum acceptable packet error loss rate, a maximum acceptable block error rate at the first transmission, and so on. A pair of communicating devices may agree that the pair of communicating devices will strive to achieve the desired QoS.
Different types of traffic may request and/or require different QoS. For example, voice communications are tolerant to lost packets but susceptible to delayed packets. Humans can “fill in the gaps” in a voice conversation due to lost packets but become frustrated having to wait for unnatural delays in conversation. Thus, a voice communication channel (e.g., VoIP, voice over Internet Protocol) may have a QoS that specifies a relatively high maximum acceptable packet loss rate but a relatively low maximum acceptable packet delay. Data communications, on the other hand, are not very tolerant to lost packets but are tolerant to delayed packets. Computers can assemble packets when the packets arrive, but computers prefer to assemble correct packets with correct data. Thus, a data communication channel may have a QoS that specifies a relatively low maximum acceptable packet loss rate but a relatively high maximum acceptable packet delay.
Different apparatuses that conform with different standards may provide different built-in QoS definitions. For example, the 3GPP (third generation partnership project) defines nine different QoS definitions (QCI1 through QCI9, where QCI stands for QoS Class Identifier) with different packet delay budgets ranging from 50 ms to 300 ms and different packet error loss rates ranging from 10−2 to 10−6. Similarly, WiMAX defines five different QoS definitions (e.g., UGS, RT-VR, ERT-VR, NRT-VR, BE). Conventionally, a CQI measurement has been made without regard to the QoS in place or desired on the channel being evaluated. Instead, a conventional mobile station may make a CQI calculation based on channel conditions only, including, for example, path loss, and frequency selectivity and interference level with specific frequency reuse factor. Using these channel conditions, the mobile station may compute the CQI so that a fixed sized packet would have a 10% block error rate (BLER). While interesting and useful, this fixed assumption CQI may be somewhat irrelevant if the base station to which the fixed assumption CQI is provided is configured to provide a different QoS with a different BLER and packet size than those used by the mobile station in the CQI computation.
A CQI is a measurement of the quality of communication occurring on a wireless channel. A high CQI represents a channel with good quality, while a low CQI represents a channel with lower quality. A CQI can be computed a number of ways and may be based on items including, but not limited to, a signal to noise ratio (SNR), a signal to interference plus noise ratio (SINR), a signal to noise plus distortion ratio (SNDR), a finite alphabet capacity (FAC) calculation, a bit error rate (BER), and a block error rate (BLER). CQI messages are sent on a mobile communication system to provide a base station with information about the channel quality. A CQI message may carry information including, but not limited to, a carrier level received signal strength indication (RSSI), a bit error rate (BER), and a recommended transport-block size. The recommended transport-block size may be communicated rather than an objective measurement of signal quality because the qualities relevant to the channel are the maximum instantaneous data rate on the channel and the error rate associated with that data rate.
Conventional systems may include a base station that makes a CQI request to a mobile station. The mobile station may then compute a CQI using the mobile station's fixed assumptions and provide the CQI to the base station. The base station may then adapt scheduling and/or modulation based on the CQI. By way of illustration, a base station may schedule more traffic on a channel that has a higher CQI and less traffic on a channel that has a lower CQI. Also, a base station may change the base station's modulation scheme for a channel whose CQI falls below a threshold. While this conventional approach is useful, this conventional approach is based on an mobile station making a single CQI determination based on generally fixed assumptions at the mobile station. Thus, the single CQI determination may not be based on available and relevant information.